Faulty Radiator Cap Lets Fluid Fly

When our first grandchild was due, we traded our campervan for a dual-cab Toyota Hilux so we could tow a caravan (you can't put child seats in a campervan). Part of the deal when we bought it (second-hand) included parts-and-labor insurance on the main engine components, and fixed-price servicing for some years. I had to travel further to work so my wife used the Hilux for short trips and I drove our two-door Mazda.

One day my wife noticed that the engine temperature was high, so we took it in for a service. The shop cleaned a few leaves out of the radiator grill and sent us home. That didn't fix the problem, so back to the shop we went. They replaced the thermostat. Then we had to go back to have the water pump replaced. Next is was the radiator. We thought we were all set, but we ended up back again, and this time we were told that the cylinder head was warped. They kept the Hilux for a week while they machined the head and re-installed it. Part of that was not covered by the insurance.

Shortly after, we were in the process of buying a new house. I had to see solicitors to sort out details, and on the way there the Hilux began to seriously overheat. We couldn't stop or we could have lost the house, so we kept going with one eye on the temp gauge. Afterward, we drove straight to the service bay and said as nicely as possible, "Fix it!" The mechanic said that it the problem must be the gauge, and then he removed the radiator cap, at which point antifreeze sprayed everywhere.

The cap turned out to be faulty. When they replaced it with a new one, the problem went away. I think the cap was drawing air instead of fluid from the overflow tank. I checked the level in the tank when cold and it seemed to be constant. My big mistake was to take the maintenance agreement instead of doing it myself.

The Hilux has been fine since -- about eight years.

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@ John: "Modern cars have radiators that are just enough to get the job done"

YES! I have confirmed that many cars lately come with the smallest/cheapest radiator available in them. Is part of the Philosophy of "if I save two cents on every car..." mantra that plagues present day economy and manufacturing. As fully new engines are free from any hard deposits and fouling, engineers (of the mokeyish style) are specifying for the least possible heat transfer area, taking advantage of the relatively high heat transfer coefficients. Some of the HTC increase is due to modern selection of fin improvements, like sliting or corrugations, but after the first few years of the car life, those fins lose the additional heat transfer capacity and the radiator becomes undersized for the requirement. As the engine wears and start to foul, the cooling system will now be undersized! and replacing the radiator with a new one identical to the original one can still overheat the engine. Another case I frequently see at auto racing and performance circles, is that, in an (futile) attempt to improve cooling an overheating modified engine, a larger transfer area radiator is fitted. But the mistake is using a three or four (or five) row radiator, that surprisingly, is still incapable of lowering the temperature of the engine. What is often ovelooked, is that by indiscriminately adding more rows of tubes several things happen: OK, larger radiator has more area... BUT, the second, third and fourth rows are less and less efficient because their temperature difference is lower and lower as they now receive warmer and warmer air from the first rows; and a factor that is mostly understimated: the transversal flow area of the added rows is now too large for the true flow capacity of the coolant pump, so that the velocity of the coolant in the multi-row radiator drops down, the flow regime is now laminar and not turbulent enough. suddenly, the heat transfer coefficient drops down to the floor, unless the pump is replaced with a special, larger flow pump. I have solved several of this cases by using a single row radiator with larger frontal area and correct flow area in the tubes. This requires one to do some fast calculations and tube measurements, and sometimes an enlargement of the cooling air area or ducting modifications, but the slimmer radiator now works way better than the specially made 4-row ones, and costs much less. A little number crunching does it.

Pressure washing the engine bay is frequently a source of trouble, but only because it can be done wrongly! Properly done it should be perfectly harmless.

First: Remove all loose grease and dirt in heavily soiled and neglected engine bays with the help of scrapers and brushes. The engine should be warm, not very hot or completely cold.

Next: use a good quality engine cleanser spray can. This facilitates the grim removal, so that it only requires a quick flush of water, avoiding the temptation to use the strong pressurized water stream as a mechanical scraper!

Then flush the already dissolved grim and dirt but using a wider angle nozzle (like a 40°) avoid using any one more concentrated, keep at least 3 or 4 ft away, nearer to the engine and the stream will be too hard on the engine components, in those cases the water can easily penetrate the seals on electronic connectors and cause damages, short circuits etc. Be gentle but still benefit from the pressure cleansing effect.

Last; and the most important: allow water to evaporate (the reason for doing this on a warm -but not hot- engine. Use plenty of compressed air to blow out any puddles on voids and places where water can collect. Dry all sparkplug wires by hand with a dry cloth, preventing high voltage streaks that are those that can damage the car's computer or electronic modules. Avoid the use of extra-shine products: they can give a contest look at first sight, but they also tend to collect any dust that settles on the engine.

As I enjoy maintaining my vehicles, I do perform all their oil changes and tune-ups at home, saving quite a few bucks and doing it much more correcly than any commercial shop. I have never had any problem following these guidelines, but have seen several cases of damaged computers at careless "quick-and-dirty" places too. and it is a real pleasure being able to work on a truly clean and shiny engine BTW. My two cents. Amclaussen.

( I think you are implying that IBM maintains a lot of dead-wood in its staff ? Hmmmm --- I couldn't comment, as I never worked there. However, if you were to make a similar accusation about Motorola --- then yes, you would be correct!! )

@ LarryM; The vacuum gauge is not necessarily a good thing. I have both a pressure and a vacuum bleeder, the pressure bleeder goes on the fluid reservoir the vacuum bleeder goes on the individual bleeder fittings-one at a time. The flexible lines going to the front wheels and to the rear-end have a outer rubber (something) cover, a braided steel layer and an inner rubber (something) layer. When you pull a vacuum on these flexible lines it is quite possible you will collapse the inner rubber layer - it will still pass fluid but it is likely to collapse in such a way that it acts like a one way check valve. Send the car down the road and after repeated applications of the brakes the pressure in the wheel cylinders cannot release and the resultant friction causes smoke and very irritated customers. I have enough experince with bleeding brakes and irritated customers that I no longer use the vacuum method. Also, flushing brake fluid should not permit air to enter the lines, thus no bubbles will be available to accumulate.

Amclaussen, I'm with you, there are few/none auto designers who care about servicability, They need to work on their own cars for a while. They have become like electronics & appliance designers who just think when it goes bad you get a new one.

I red somewhere that automotive assembly effenciency experts, hahaha, don't like screw threads because the only worthwhile turn the fastener makes is the last one when it tightens. They would replace everything with push on fasteners, try taking that in & out several times.

Yes, the cap is easily over looked and probably not replaced ofent enough. I have always wondered how much of the cooling system is thermal syphin dependant. Our 1913 Overland is 100% thermal syphin, no water pump, and keeps the 4 cylinder engine cool. Modern cars have radiators that are just enough to get the job done. I know radiators are really poorly made and some are better built than others even if they look exactly alike. I replace the radiator 3 times in my 96 cadillac. Twice with a radiator from AutoZone's expensive unit and the last time was charm. It was cheaper and came from a radiator shop. The pet cock on the bottom kept blowing the square rubber ring that sealed the valve.

Not to be a Monday-Morning Quaterback, but checking the radiator cap is always one of the first checks, right after leaking hoses and thermostat.

I had a similar situation on my '01 PT Crusier. The overflow bottle would fill up but not empty back into the radiator as the car cooled. I went over quite a lot of possible solutions, including leaking hoses, etc... including pressure testing the radiator cap, but the solution was found by vacuuming testing the cap. And a new aftermarket replacement ALSO had the same problem!

I also had the problem that the cap would remain under pressure (vacuum?) when the car cooled down and was difficult to remove. BTW, try never to let the temp get much higher than on click above normal. Besides warping the heads, pressure failure/leaking of the heater core can happen quickly. (I know from personal experience). In the above example, my heater core started leaking around where the supply pipes were connected to the core. Replacing the leaking core was a chore an a half. I swear that cars are built starting from the heating/AC units out.

Seeing as we're on the engine/temperature topic, I recently discovered a quick way to destroy a diesel fuel injection pump $$$. As you may know the tolerances inside one of these pumps are very tight - so tight that if you warm the rotor in your hand, it will no longer fit into the collar, I've been told. The working pressure of injection nozzles is around 200 atmospheres or 3,000psi. The rotor part of the distributor in the pump is a vertical cylinder with a series of radial holes each of which lines up with a specific fuel injector's line. The collar that surrounds this rotor has holes that lead to each of the fuel injectors. - no seals at those rotation speeds and pressures - tight tolerances are the rule.

If you have a diesel truck, tractor or combine and have had an especially dirty day out in the field, the temptation is to clean things up with a high pressure washer. I've been farming for 39 years, and nowhere in any of the manuals does it warn you not to do that. You have a hot injection pump whose outside collar you cool down and shrink fit on to the rotor, gouging things up, and breaking the drive. The fuel injection shop crumpled two snap-on sockets trying to press the two pieces apart and finally had to torch them apart. The fuel injection tech was good enough to tell me that hosing down a hot fuel injection pump is the number one cause of catastrophic pump failures ($1,600 in my case). In my 39 years of farming I've had three such experiences without realizing what was going on. Make sure your engine is cold before you hit it with water, and then let it stand for a good while to let temperatures equalize before you start it up again. A hard lesson to learn - you may want to pass it on to your diesel powered friends.

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